Frontrunner wins California and three other states to become the first female presidential nominee of a major US party.

Road to the Democratic nomination

Hillary Clinton takes New Jersey, South Dakota, New Mexico and declares victory

Bernie Sanders wins in North Dakota

Two more states, including the biggest- California, have yet to announce

Sanders rejects AP's declaration calling the race for Clinton

Democratic frontrunner Hillary Clinton has laid claim to the party's presidential nomination after a series of victories in primaries.

Clinton won resoundingly in California, the largest state in the US and a key target of her opponent, Bernie Sanders. With 93 percent of precints reporting, Clinton won 56 percent of votes cast and Sanders 43 percent.

Clinton also took the states of New Mexico, South Dakota, and New Jersey on Tuesday evening before declaring victory over Sanders for the Democratic Party nomination. Sanders won North Dakota and Montana states.

Serving US President Barack Obama called Clinton to congratulate her on securing enough delegates to clinch the nomination.

"Thanks to you, we've reached a milestone," she said at a rally in New York, before taking aim at her likely Republican competitor, Donald Trump.

Clinton told supporters in New York that Trump was "temperamentally unfit" to be president, citing Trump's attacks on a federal judge, reporters and women.

"He wants to win by stoking fear and rubbing salt in wounds and reminding us daily just how great he is," Clinton said.

"Well, we believe we should lift each other up, not tear each other down."

Sanders has vowed to continue his campaign to next week's primary in Washington DC and further to the convention held in Philadelphia on July 25.

"The fight in front of us is a very, very steep fight but we will continue to fight for every vote and every delegate," he told a rally in Santa Monica, California.

Clinton declaration of victory comes a day after the Associated Press announced she was the presumptive Democratic nominee based on a count of elected pledged delegates and unelected superdelegates.

The Sanders campaign rejected that announcement as premature and said it would continue to campaign in California.

In an interview with NBC News, Sanders expressed concern that the news of Clinton's victory came the night before "the largest primary" and that it was based on what he described as "anonymous" commitments from superdelegates, who vote at the Democratic convention in late July.

"They got on the phone, as I understand it, and started hounding superdelegates to tell them in an anonymous way who they were voting for," he said.

"The night before the largest primary, biggest primary in the whole process, they make this announcement.

"So I was really disappointed in what The AP did."

Sanders is set to meet Obama at the White House on Thursday, the Reuters news agency reported.